Most sinks have an overflow vent to catch rising water and divert it to the drain before the sink overflows. Unfortunately, water that gets into the overflow vent may not fully drain, allowing bacteria to grow in the overflow vent. When water passes through the drain during normal use, air may be forced through the overflow vent past this bacteria and out into the air around the sink. This can become a health risk, particularly in public-use sinks such as public restrooms, hospitals, and other sinks that may harbor harmful bacteria.